REFERENCES 1. The section on topography of the mountain section is taken largely from Water-Supply Paper No. 469 of the United States Geological Survey. 2. Section on geology and soils taken largely from Water-Supply Paper No. 469 of the United States Geological Survey, and from the Soil Survey Report of Western Nebraska of the Bureau of Soils. 3. Information on climate secured largely from United States Weather Bureau publications. 4. From article by Ivan E. Houk, Evaporation on United States Reclamation Projects, January, 1926, number of the transactions of the American Society of Civil Engineers. 5. From Department of Commerce bulletins, giving census of agriculture for Colorado and Wyoming in 1925. 6. Page 48 of Nebraska Resources and Industries, Bulletin 14, of the Nebraska Conservation and Soil Survey Department. 7. Article by F. R. Johnson, in December, 1922, issue of Water Resources, entitled "The Influence of the Forest in Retarding Runoff," etc. 8. Taken from paper No. 1589 of the transactions of the American Society of Civil Engineers, Flood Flow Characteristics, by C. S. Jarvis. BIG SIOUX (Area 61) LOCATION AND AREA The Big Sioux River drainage area includes (1) a comparatively narrow strip of territory, varying from less than 1 mile to about 42 miles wide, along the eastern side of South Dakota, extending from the extreme southeastern corner of the State northward for a distance of about 200 miles, covering an area of 5,172 square miles within South Dakota; (2) a triangular-shaped area of 1,353 square miles in the extreme northwest part of Iowa, lying mostly northward from Sioux City; and (3) a triangular-shaped area of 1,687 square miles in the extreme southwestern corner of Minnesota, which area extends eastward along the south boundary of Minnesota about 40 miles and northward along its west boundary about 66 miles. The total area within the watershed is 8,212 square miles. TOPOGRAPHY In general this region may be classed as a plains area, having a general southerly slope. Along the southern part of this drainage the hills and bluffs are comparatively high, rising 100 to 300 feet above the river valley. The elevation of the lowest part near Sioux City is 1,100 feet. From this point there is a gradual rise to an elevation of around 1,800 feet in the northern part. The Sioux River, irrespective of the falls and rapids near Sioux Falls, has a gradient of more than 2 feet per mile. That portion of the area in Iowa and Minnesota, as well as in the northern part within South Dakota, is a level to rolling upland prairie. The entire area is cut by numerous streams and water courses, some of which are narrow, others broad and flat. In portions of the watershed the drainage is rather incomplete and many lakes are scattered over the area. The Big Sioux Valley lies between glacial moraines on the east and west. In Brookings County, S. Dak., which is a fairly typical midway cross section of the area, the drainage consists of rolling and level upland prairie cut by numerous stream valleys. GEOLOGY AND SOILS (A) Geological formations.-The surface formations belong to the glacial period. There are a few outcrops of basal rock in portions of the Big Sioux Valley. These outcrops consist chiefly of Sioux quartzite belonging to the Algonkian formation. Practically the whole area is covered by glacial drift of varying depths, the result of one or more glacial invasions. The material deposited in this manner is a mixture of clay, sand, pebbles, and bowlders. Overlying the glacial deposits is a fine porous clay, called "loess." This formation is distinguished from the glacial deposits by its lack of pebbles and bowlders. Both this loess and glacial material are subject to erosion much more readily than are the underlying formations. (B) Soils. The soil of this region is quite uniformly a loam derived from the glacial deposits and the loess as subsoils. The valley floor of the main rivers is filled with sands and gravels overlain by an alluvial soil. The bottom lands of the Big Sioux River above the Missouri have an average width of about 2 miles. The soils in this region are comparatively easily eroded, as is indicated by the increasing depth of the river valleys as they near the Missouri River Valley. That portion of the Iowa glacial sheet exposed in this area shows the effect of greater erosion and longer weathering and gives rise to soils containing more sand than those of the Wisconsin glacial sheet. The soils, as a rule, become more heavy and loamy as the moraines on each side of the Sioux Valley are approached. The most serious erosion which has occurred is the ruining of farm land due to caving of river banks which is not, however, excessive. Very little waste land is found in this unit except river wash and dune sand. CLIMATE The For the general region eastern South Dakota and northwestern Iowa, the average annual precipitation is about 25 inches. greater portion of this falls within the crop-growing season, more than three-fourths of the annual total being received within the six months, April to September, inclusive. The greatest monthly precipitation usually occurs in June, closely followed by May and July. The greatest annual averages are in the southern counties east of the Missouri and in northwest Iowa. The average annual rainfall of the South Dakota portion of this area is sufficient for the production of good crops, but the variability of the precipitation during the growing season is often a serious matter. In an occasional winter there is a heavy snowfall and the snow on the ground accumulates to a considerable depth, but as a rule, the snow covering over the State during the winter is not great. The average annual temperature is rather low, the Weather Bureau records indicating an average of about 46° for the area, with an average annual range of about 136°. The winters are long and severe. The cold, however, is rendered less noticeable by the dryness of the air. The winds are a very important climatic factor of this region, strong winds being very frequent in every season of the year. From December until March the prevailing direction of the wind is from the northwest or north, resulting in blizzards and very low temperatures. Evaporation data are not available. HISTORICAL DEVELOPMENT Fur trading with the Indians was the first industry of this territory and was quite profitable until about 1878, when the settling up of the country resulted in the disappearance of the game. Although trading posts were established in this region by the early French fur companies, the Indians were hostile to settlers and there was little agricultural development west of Big Sioux River until about 1862, when treaties with Indians made this land available. The early settlers made their homes along the Sioux River. This was done in order to take advantage of the narrow strip of timber along the stream, and because of the protection from prairie fires which the river afforded. Prairie fires were of frequent occurrence and were a source of great danger and loss to the settlers so long as the prairie remained unbroken. About 1872 the line of the Chicago, Milwaukee & St. Paul Railway was built into southwestern South Dakota, and by 1880 the territory had been largely homesteaded. This drainage area is primarily an agricultural section, producing large acreages of corn, wheat, and oats. Native hay is produced in nearly all parts of the upland on poorly drained lands. There are neither extensive forests nor large bodies of water in this area. In the Big Sioux Valley there are numerous small groves of timber, principally cottonwood, box elder, and ash, ranging from 1 to 10 acres or more, in areas that have been planted and cared for by farmers. There is very little natural timber found in the area and such as is found is in the form of narrow fringes along the streams. The country is naturally a prairie region. The timbered area has been increased to a small extent by the planting of groves. There is a limited acreage of woodland being cleared for crops, but on the whole there is little change taking place. CONDITION OF LANDS OTHER THAN FOREST (a) The 1925 agricultural census shows that 90 per cent of this area is included within farms and that approximately 69.3 per cent of the area is classified as crop land, producing corn, wheat, oats, flax, and potatoes, and hay as the principal crops. Cultivation of the soil is such as to store up as much of the rainfall as possible and the runoff is reduced proportionately, resulting in a low degree of erosion. (b) The unimproved lands include chiefly the rougher lands and grassland areas used principally for pasture. This class will include about one-fourth of the whole unit. On these unimproved lands the cover of grasses and other vegetation gives effective protection against erosion which on a bare surface would be excessive. The grassland areas are pastured and there is no longer a serious fire problem. The tendency is more often toward overgrazing which results in some erosion and gullying. The area is quite well drained naturally and artificial drainage is unnecessary. CONDITION OF FOREST The forest area within this unit is very small. The timber consists only of the one type-upland hardwoods, and its proportion of the area is, according to 1925 agricultural census figures, approximately 0.86 per cent. A. Cutting for lumber has never been of consequence here, although early settlers used limited amounts of the native timber for buildings. B. Forest fires have not been a problem and little damage to timber has resulted from that cause. C. Grazing of woodland areas is quite generally the practice in this unit and has been more or less detrimental to the timber itself, especially in damaging young reproduction by trampling and browsing. Trails made by the stock are the first place in which erosion takes place. This is especially true on the steeper slopes. D. Drainage by artificial means has not been necessary and very little of it has been done. Mention is made in one of the soil-survey reports of the existence of several feet of water in certain depressions when settlers first came to the region. Such places are now dry. This is explained by the gradual lowering by erosion of the level of the soil surface at the outlets and surplus waters are readily drained off at the present time. E. In general, the forest conditions are such in this unit that their influence and value are largely of very local application. Planted timber about farm buildings and a limited area of natural timber along the streams comprises the woodland acreage. Cottonwoods, box elders, and ash are the predominating species of hardwoods. Red cedar is the only native conifer. All these are growing in open, scattered stands and are of inferior quality. Protective value of the watershed Rated as follows: (a) Soil: Loam soil, 100 per cent of area, rated at. (b) Topography 75 80 per cent of area practically level, rated at 100 80 20 per cent of area steeper slopes, rated at 50 per 10 90 (c) Precipitation 50 per cent of rainfall in heavy downpours, rated 25 50 per cent of rainfall in form of snow and gently 50 (d and e) 34.65 per cent of the area in corn, potatoes, etc., The average rating as shown above is comparatively high for this section, resulting from the rather flat relief with its loam soil, which is not appreciably eroding in any place. A heavy percentage of the total area is crop land, producing varied crops, with corn among the principal crops grown. The area in pasture and hay land makes up the greater portion of the unimproved lands, with forested areas of less than 1 per cent. The area does not have a high annual precipitation and conditions are not serious from the standpoint of excessive run-off and erosion anywhere within the unit. CRITICAL FOREST AREAS There are no data available indicating within this area the existence of any critical areas as affected by erosion or flood conditions. The forest area is very small but there are unquestionably many small local areas which individually might be considered as critical. Information as to this would not be obtainable except through careful survey of the areas in question. All such possible areas are on private lands and in most cases corrective action, if taken, will depend upon the value of the area to be protected and the cost of the work necessary. Forest planting for protection of watersheds or eroding lands has in reality been given very little, if any, attention in this region. As a whole, however, there are no areas which, from the standpoint of erosion and flood control, are recommended as critical. RECOMMENDATIONS FOR THE WATERSHED A. The area to be retained in forest should, under no conditions, be permitted to become less than at the present time. The present forest area, as shown by the 1925 agricultural census figures, is but 0.86 per cent. This small percentage expressed in actual area amounts to but 44,031 acres. This percentage in forest is but little changed from the original native woodland area found by the early settlers. Some lands have been cleared and placed under cultivation, but planting of windbreaks and groves on farms has helped to maintain the original area. B. At present fire protection is not a serious problem within this region. Very little fire occurs in timber and the individual owners in each case now assume the responsibility for protecting their own timber. Protective measures against other agencies, such as insects, disease, etc., are largely unnecessary. Assistance can usually be secured from the State agricultural colleges. Proper methods of cutting and management to insure prompt restocking are important to prevent decreasing of the forested area. The State should have some control over such cuttings. |